Engineered VP1 mRNA Vaccine Induces Immunity and Complete Protection Against Feline Calicivirus in Cats

Feline calicivirus (FCV) is a major pathogen of upper respiratory tract diseases in cats, posing a significant threat to feline health. While current FCV preventive measures rely primarily on traditional vaccines, messenger RNA (mRNA) vaccines have emerged as a promising alternative, offering high efficacy, safety, rapid clinical development, and potential for fast, cost-efficient production. In this study, we designed a modified nucleotide sequence with a 124-amino acid deletion at a position in the region of the FCV-VP1 protein as an immunogen. The plasmid encoding the codon-optimized VP1 sequence was constructed, and VP1-mRNA was generated by in vitro transcription (IVT) and capping. After transfection into BHK-21 cells, immunofluorescence assay (IFA) and WB confirmed successful FCV-VP1 expression. Subsequently, the mRNA was encapsulated into lipid nanoparticles (LNPs) to prepare the LNP-VP1-mRNA vaccine. Characterization analysis revealed a uniform particle size distribution (polydispersity index [PDI] = 0.169) and a stable surface charge (zeta potential = -1.67 mV). A prime-boost immunization strategy was employed, which involved two intramuscular injections to immunize BALB/c mice or cats with the LNP-VP1-mRNA vaccine. ELISA analysis demonstrated that the vaccine elicited elevated levels of anti-FCV IgG and neutralizing antibodies in a dose-dependent manner, accompanied by the secretion of cytokines including IFN-β, IFN-γ, IL-4, and IL-6. Importantly, the VP1 mRNA vaccine provided complete protection against FCV challenge in cats, without the typical clinical signs and with a 100% survival rate. Our results indicate that the LNP-VP1-mRNA vaccine is a promising candidate for combating FCV infection.